This invention relates to producing a pressure-responsive surface upon paper, metal, plastic and other substrates, especially a surface for printing by application of low to moderate impact or pressure, such as developed by a typewriter letter-face in normal operation or mechanically by a press or the like, or by hand using a stylus or the like pointed rods.
Comparatively little attention has been given in the past to the effects of pressure upon diacetylenic compositions. U.S. Pat. No. 3,501,302 of Mar. 17, 1970 to Foltz discloses certain effects of pressure on certain diacetylenic monomers. Specifically at column 5, line 65 to column 6, line 39 the Foltz patent discloses photo sensitive polyyne compounds which are photopolymerized when irradiated and thereby become colored, usually blue or purple; and change to red on heating or extraction by a solvent. These products are pressure-sensitive in that they become a dark blue when subjected to high pressures such as 10-20 kilobars of pressure (i.e. about 1 to 2 million kPa). Moreover the patent at column 24, lines 1-11 discloses filter paper saturated with an ether solution of 13,15-octacosadiyne and aged about one week, then subjected to slight pressure as by scratching with a stylus or striking with a letter-type face, and immediately thereafter exposed to ultraviolet light. Thereupon that portion of the filter paper at which the scratching or pressure was applied is described as immediately taking on a deep blue coloration. p U.S. Pat. No. 3,999,946 of Dec. 28, 1976 to Patel et al. at column 9, lines 29-42 indicates that the compound 2,4-hexadiyn-1,6-bis(phenyl urethane) changes color at a rate depending on temperature and thus can be used as an indicator of cumulative effects of time/temperature. Moreover, this passage indicates that when said compound is deposited from dioxane solvent, it can be inactivated by subjecting to stress such as exerted by stamping with code numbers, so that the indicator regions under each stamp will be deactivated against further color change, at the time of stamping. (Per Example 1, at first the color is blue, which intensifies; and then, at 40.degree. C. and above, changes to red).